Carbon nanotubes (CNT) have been the subject of intense research since their discovery in 1991. CNT's possess unique properties such as small size and electrical conductivity, which makes them suitable in a wide range of applications, including use as structural materials in molecular electronics, nanoelectronic components, and field emission displays. Carbon nanotubes may be either multi-walled (MWNTs) or single-walled (SWNTs), and have diameters in the nanometer range. Depending on their atomic structure CNT's may have either metallic or semiconductor properties, and these properties, in combination with their small dimensions makes them particularly attractive for use in fabrication of nano-devices.
One of the drawbacks to the implementation of CNT's in nano-device fabrication processes is the difficulty in obtaining samples of CNT's that have uniform lengths, or chirality. Additionally, no facile method is available for the immobilization and manipulation of CNT's for nano-device fabrication.
Most methods of CNT synthesis produce a product that is a mixture of entangled tubes of “ropes”, giving CNT's differing in diameter, chirality, and in the number of walls. Various methods such as acid washing, ultra-sonification, polymer wrapping and use of surfactants have been employed for nanotube separation (J. Liu et al. Science 280, 1253 (1998); A. G. Rinzler, Appl. Phys. 67, 29 (1998); A. C. Dillion et al. Adv. Mater. 11, 1354 (1999); (Schlittler et al. Science 292:1136 (2001)).). However, there has been no report of a method for the specific disentangling of nanotube ropes or their separation into populations having discrete sizes, chirality or conducting properties.
Because of their ability to specifically recognize substrates, various proteins represent one possible route to solving the CNT separation/purification problem as well as providing a possible means for CNT immobilization. Some attempts have been made to raise antibodies to various carbon based structures. For example, Chen et al. (WO 01/16155 A1) used conjugated fullerenes to raise monoclonal antibodies to C60 fullerene as a hapten. However, the population of antibodies raised by immunization of mice with this C60 fullerene derivative which was conjugated to bovine thyroglobulin included a sub-population that cross reacted with a C70 fullerene. No attempts have been made to date to raise antibodies to carbon based nanotubes.
Since its introduction in 1985 phage display has been widely used to discover a variety of ligands including peptides, proteins and small molecules for drug targets. (Dixit, S., J. of Sci. & Ind. Research, 57, 173-183, 1998). The applications have expanded to other areas such as studying protein folding, novel catalytic activities and DNA-binding proteins with novel specificities. Whaley et al (Nature, 405:665 (2000)) has used phage display technique to identify peptide sequences that can bind specifically to different crystallographic forms of inorganic semiconductor substrates. Although the method of generating large, diverse peptide libraries with phage display has been known for some time, it has not been applied to the problem of finding peptides that may be useful in the binding and manipulation of CNT's.
The problem to be solved, therefore, is to provide materials that have binding specificity to CNT's and other carbon based nanostructures so that they may be used in separation and immobilization of these structures for the fabrication of nano-devices. Applicants have solved the stated problem by providing a series of carbon nanotube binding peptides with high affinity and specificity for CNT's.